Sunday, August 5, 2012

Basic Error Handling in Perl

Anyone that has ever sat at a computer help desk quickly
becomes aware of just how many issues a user can have with even the seemingly
easiest and most user friendly software around.Whether it is the user that “lost” his email because he clicked on one
of the sort buttons and now can’t find today’s messages or the user who manages
to crash a calculator-like program because he decides to type “two” instead of “2”,
it becomes readily apparent that computer users will often do things that many
developers would find unthinkable.It is
important that software developers learn this lesson early in their
career.Whether for malicious reasons or
innocuous ones, your application will be abused by those that make use of
it.While some previous posts discussed
the basics of input
validation and some modules
that could be used to perform input validation, these are not the only
useful techniques to consider.Error handling is also a useful technique for dealing
with potentially problematic situations that could arise.For example, perhaps your application
requires access to a file on removable media for certain functions or
connection to a certain network resource.While an “or die” type statement alone could be used to deal with the
situation, error handling may provide you with a way to allow your application
to route around the error or to at least fail gracefully.The basics of Perl error handling is the eval
statement, which is used as follows:

The above code works because if the code in the eval block
executes it will return true, otherwise it will return false, and cause the
code contained in the do block to execute.The above example, forces the do block to execute by intentionally
dividing by zero.

It is also notable that there are several Perl modules that
are highly useful for error handling as well such as Exception::Class,
Error,
and TryCatch.These modules will be looked at in more
detail in a future installment.

1 comment:

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